The long-term objective of the research program described in this proposal is an understanding of the genetic circuitry and cellular mechanisms that control the development of the adult peripheral nervous system (PNS) of Drosophila. The basic experimental approach is to investigate the action of specific genes and gene products required for normal sensory organ patterning and/or cytodifferentiation. The proposal concerns the genes Hairless and Bearded. Loss-of-function mutations of Hairless cause the failure of sensory organ precursor cell development. Bearded mutations appear to interfere with two successive inhibitory cell-cell interaction events during sensory organ development. Using techniques of classical and molecular genetics, cell biology, and biochemistry, we propose to analyze these genes, their products, and their functions, and to identify and study new interacting genes that act in the control of PNS development. The project has the following specific aims: (1) Molecular characterization of the Hairless gene and its RNA and protein products and analysis of their spatial and temporal patterns of expression. (2) Completion of the analysis of the Hairless null developmental defect. (3) Identification and genetic/developmental analysis of loci interacting with Hairless. (4) Molecular analysis of the Bearded gene and its patterns of expression, and biochemical studies of the interaction of the Bearded protein with calmodulin. (5) Identification and genetic/developmental analysis of loci interacting with Bearded loss- and gain-of-function alleles.